Late Onset Alzheimer's Disease

Inclusion Criteria:

* Established diagnosis of definite or probable AD or have a diagnosis of a related neurodegenerative disorder such as Frontotemporal Dementia (FTD) or Lewy Body Dementia (LBD) (will also recruit sporadic FTD and LBD) cases.
* a living sibling with probable or possible AD;
* a third living relative affected with AD (onset age 50 or older) or unaffected (60 or older);
* participants in the proband's generation with an identified companion serving as an informant;
* participants who have capacity to consent or participants lacking capacity to consent with a surrogate/proxy in place to provide consent.

Exclusion Criteria:

* failure to identify an appropriate informant;
* uncertainty of the clinical diagnosis of Alzheimer's disease or other related disorder;
* discovery of additional diagnosis that could account for the clinical manifestations;
* unwillingness to participate;
* failure to identify a living sibling with AD or other related disorder (except in the cases of sporadic FTD and sporadic LBD);
* participants lacking the capacity to consent who do not have a surrogate or proxy or next of kin to provide consent.